1. Technical Field
The present invention generally relates to polymer gels, polymer cryogels, activated carbon materials, and methods for making the same.
2. Description of the Related Art
Activated carbon is a highly porous form of elemental carbon, typically having a surface area of at least 500 m2/g. Activated carbon materials are useful in many different applications. For example, activated carbon materials are used, inter alia, for chemical adsorption, gas storage, heterogeneous catalysis, and in energy storage devices. Given the broad demonstrated utility of activated carbon materials, efficient methods for their production are needed in the art.
One traditional approach to produce high surface area activated carbon materials, such as for use in ultracapacitor electrodes and other energy storage devices, has been to pyrolyze an existing carbon-containing material (e.g. coconut fibers or tire rubber). This results in a char with relatively low surface area which can subsequently be over-activated to produce a material with the porosity necessary for the desired application. Such an approach is inherently limited by the existing structure of the precursor material. This approach also typically results in low process yields due to removal of a large portion of the original char during the activation step.
Another approach for producing high surface area activated carbon materials has been to prepare a synthetic polymer from carbon-containing organic building blocks (e.g. a polymer gel). As with the existing organic materials, the synthetically prepared polymers are pyrolyzed and activated to produce an activated carbon material. In contrast to the traditional approach described above, the intrinsic porosity of the synthetically prepared polymer results in higher process yields because less material is lost during the activation step. In addition, some control over the pore size distribution of the final activated carbon material can be exerted by using different building blocks and/or polymerization conditions.
Although preparing activated carbon materials from synthetic polymers has several advantages over pyrolysis and activation of existing precursor materials, the known methods have several disadvantages. For example, preparation of activated carbon materials from synthetic polymers typically requires a time-consuming and expensive solvent exchange step prior to supercritical drying or freeze drying. Furthermore, the dried polymer material (e.g. polymer cryogel or aerogel) typically contains a residual amount of organic solvent. A viable manufacturing process for activated carbon materials must overcome these and other limitations of the existing methods.
While significant advances have been made in the field of activated carbon materials, there continues to be a need in the art for new and improved carbon materials and related methods. The present invention fulfills these needs and provides further related advantages.